Attrition scrubbers are in wide use in industry and are typically employed in processes such as particle cleaning or the like. For example, the glass industry has utilized attrition scrubbers for many years to remove surface contamination from silica sands in order to improve the clarity in glass. Attrition scrubbers operate to effectively remove the surface contamination by rubbing or grinding down the particles. The aforementioned rubbing or grinding down creates friction forces, also known as shear forces, which separate the undesired contamination from the desired glass.
Attrition scrubbing, specifically hydraulic shear attrition scrubbing, is a process by which particles are scrubbed by thrusting the individual particles into one another at high speeds. The friction created by the high speed collisions functions to effectively shear the undesired material, for example surface contamination, from the desired material. Due to the aforementioned collisions and resulting friction, little wear occurs on the machine itself because scrubbing is accomplished by friction that is created by particle-to-particle collision, not machine-to-particle collision.
Oftentimes the aforementioned scrubbing process may require multiple stages depending upon the desired degree of separation or desired process staging. In these multiple stage processes, both the undesired material and the desired material are combined into a single medium. The medium is then subject to a series of attrition stages. As the medium graduates from stage to stage, a higher degree of separation is achieved among the desired and undesired material.
One way of achieving the desired degree of separation involves employing multiple attritioning cells in a side-by-side arrangement. In these arrangements, each attritioning cell usually has two oppositely arranged impellers mounted to a rotatable shaft. As the impellers are rotated, they force the liquid medium to flow in opposing axial directions, thereby creating particle-on-particle impact.
The aforementioned multiple staging processes have drawbacks however. The multiple staging attrition scrubbers are typically configured wherein the cells are positioned in a side-by-side arrangement, causing the attrition scrubbers to have a very large footprint and consume a large amount of floor space. Also, due to this side-by-side arrangement, multiple shafts and multiple attrition drive motors are required, which can be costly. Also, in order to obtain the desired degree of separation, a large amount of energy must be transferred to the particles. This energy transfer is typically accomplished by rotating the impellers at very high speeds, which consumes a large amount of energy. Thus, the more shafts that must be rotated at a high rate of speed, the more energy that is consumed during operation of the attrition scrubber.
Accordingly, it is desirable to provide an energy efficient attrition scrubber apparatus and method having a reduced footprint that achieves a desired degree of separation.